Introducer devices provide for access to the vascular system. They are employed for inserting medical devices such as catheters, guidewires, leads, infusion ports, dialysis ports, dialysis catheters, and other such devices into the vascular system. A typical procedure for gaining access to the central venous system or the arterial system with an introducer is the Seldinger Introduction Method. The Seldinger Method provides for insertion of a hollow needle into the vasculature of a patient. A guidewire is inserted through the needle, and the needle is removed over the guidewire, leaving the guidewire in the vessel. The introducer assembly including the dilator and the introducer sheath is inserted over the guidewire into the vessel. The introducer assembly is advanced into a suitable position within the vessel, i.e. so that the introducer's distal end is well within the vessel but the proximal end of the introducer assembly is outside the patient. With the introducer assembly in the vessel, the guidewire and dilator are removed sequentially, leaving only the introducer sheath in the vessel. The introducer sheath is left in position and therefore offers direct access from outside the patient into the blood vessel lumen. The desired medical device is inserted through the lumen of the sheath into the appropriate vessel, and is implanted at the desired location within the body. To minimize any disturbance to the medical device, the sheath is removed from the medical device by cracking apart the handle, and peeling apart the sheath. Such removal techniques are well known by those skilled in the art.
During insertion of the introducer assembly including the dilator/introducer sheath into the body along the guidewire, the distal end of the introducer has to pass through various types of body tissue and anatomy. Sometimes the body tissues are rigid. This can cause significant resistance to movement of the introducer assembly through the vasculature. If resistance is great enough, the distal portion of the introducer sheath can be damaged, resulting in an introducer that may not be able to be inserted to its desired location in the body, or that could become damaged to a point that it is non-functional. The larger the diameter of the introducer sheath the greater the opportunity for the introducer to encounter resistance as it passes through body tissue.
To reduce the chance of such damage being caused by different anatomical tissues during insertion of an introducer assembly, the distal ends of the introduce sheath and the dilator received therein are designed with tapers that provide a transition from the larger diameter portion of the introducer sheath to a more distal portion of the dilator having a reduced diameter with the tapered profile. While the tapers generally allow the introducer to enter the body with reduced resistance, the tapered transition between the introducer sheath and the dilator in an introducer assembly is still a primary source of resistance. When the cross sectional area of the transition between the dilator and introducer sheath increases, for example, when only the tip of the dilator bends in a curved blood vessel during insertion while the introducer sheath maintains a relatively straight shape, the resistance from this transitional area can increase significantly.
What would be desirable is an introducer assembly comprising a dilator/introducer sheath designed to have minimum resistance at its tapered distal end during insertion into the body. What would also be desirable is easy removal of the dilator from the sheath after insertion of the introducer assembly into the body.